Collision detector



DVCC. 6, B. L. CRE-W QOLLISION DETECTOR Filed March 5, 1960 CDA/7,90! [JET United States Patent O 3,290,666 COLLISION DETECTOR Beverly L. Crew, Phoenix, Ariz., assignor to Sperry Rand Corporation, New York, N.Y., a corporation of Delaware Filed Mar. 3, 1960, Ser. No. 12,585 7 Claims. (Cl. S40-174.1)

This invention relates to means for detecting undesired collisions 'by a magnetic head with a magnetic drum and, in particular, relates to means for detecting certain types of contacts of aying'head with its magnetic drum with provision to send an alarm in such event.

In modern data handling systems, large quantities of data are stored on magnetic drums to handle the flow of data necessary for Various business and scientific applications. The magnetic drums store these' large quantities of data in the form of a plurality of magnetized areas. A magnetic drum stores data, in the usual fashion, by the use of a plurality of tracks about its periphery. Each circumferential track contains binary coded information in that an element of the track can be magnetized ineither one of two directions.

For purposes of accuracy, it is desired that the track element reliably indicate its particular magnetizable state.

The information on a magnetic drum can lbe written on or read from the drum -by a flying head at high speeds. The ying head normally does not come in contact with the `magnetic `drum but is floated above the surface of the drum by a thin lm of air. Slight irregularities of the surface of the drum are compensated by the film of kair which keep-s the head `away from the drum by a reasonably constant distance.

Various factors, such `as dust, dirt, and other impurities between the surface of the drum and the head, eX- cessive vibration and other causes may cause the flying head to hit the surface of the drum to tend to damage the information stored in the element of the drum. A hit, also, may tend to damage the head. `Both a damaged head and damaged information are undesirable.

It is a purpose of this invention to describe a novel means for detecting undesired hits (collision of a drum with a head), to raise the head -in the event of such detection, and to otherwise indicate that an undesirable hit took place.

It is an object of this invention to provide a novel collision detector.

It is another object of this invention to provide a novel magnetic head and drum collision detector.

A further object of this invention is to provide a novel means for detecting undesirable collisions of a flying magnetic head with a magnetic dr-um and to raise the head in the event of an undesirable collision.

In accordance with this invention, there is provided a magnetic drum and a flying magnetic head of known design. A head lowering and raising mechanism also of known design which is controlled by a control network lowers the head into engagement with the magnetic drum (separated hy a thin film of air) and raises the lhead away from engagement with the drum. A hit detector network detects undesired hits and signals the control network to raise the heads. The hit detector includes ia voltage source which is applied to a high resistance lead that is attached to the magnetic head. The output of the lead from the magnetic head normally remains at a fixed potential level; however, when the magnetic head collides with the magnetic drum, the lead is grounded, thereby providing no output voltage on the lead.

The lead from the magnetic head -is coupled to one input of a two-input and gate yand to a delay ilop, or one-shot multivibrator.

The set output of the delay flop 3,290,666 Patented Dec. 6, 1966 is integrated by an integrator and applied to the second input of the and gate. The output of the and gate indicates an undesirable hit. This output can be applied to set a flip-flop, the output of the llip-flop being connected to the control network. The ilip-iiop can be reset by a clear or reset signal.

The novel features of this invention and other objects and advantages thereof, together with its organization and method of operation, will become more apparent from the following description, when read in connection with the accompanying drawing, in which the sole figure is a 'block diagram of an embodiment of this invention.

Referring to the ligure, there is shown a pair of magnetic drums 101 and 301 also labeled A and B. The drums are rotated at a high rate of speed by means not shown. Communicating with each `drum is a magnetic head 102, 302. The detection of lan undesirable hit raises both the associated heads 102, 302 respectively. The circuitry `shown in the ligure detects independently and cooperatively undesired hits in either or iboth drums 101, 301. As shown in the gure, a voltage line 203 from a positive potential source -|V has 4twobranches. One branch of the line 203 is vcoupled to the head 102 and then to a buffer 104 and to one input of ar two-input and gate 1,05. Another branch of the line 203 is coupled to the head 302 and then to a buffer 304 and to one input of a second two-input and gate 305. The two branches are labeled Hit A and Hit B respectively. rlhe outputs of buifers 104, 304 are coupled together to the set input of 4a delay op or one-shot multivibrator 206. The set output of the delay llop 206 provides `an output for a ixed period of time upon being set. The set output of the delay flop 206 is integrated by an integrator207. The output of the integrator 207 is connected to the second inputs respectively of the gates 105, 305. The output of the gate 105 is connected to the set input of a flip-flop 108. The output of the gate 305 -is connected to the set input of a flip-flop 308. A reset or clear signal on the line 209 is connected to the reset inputs of the ilip-ops 108, 308. The l or set output terminals of the llip-ops 108, 308 are connected through respective buffers 110, 310 to the control network 211. A flip-op is a bistable multivibrator, or electrical switch, which provides an output enabling signal at its l output terminal upon the application of an enabling signal at its set input terminal. The Hip-flop continues to provide an output enabling signal -at the l output terminal until an enabling signal is subsequentlyl applied to the reset terminal of the flip-flop. The control network 211, upon being actuated -by the outputs of the flip-ops 108, 308, activates the heads raising and lowering mechanism 212 to raise the heads 102, 302. The heads 102, 302, subsequently, can be transported by means of a carriage, not shown, longitudinally along the axis of the drums to a landing track. The landing track is a track on the drum which contains no information. The heads remain at the landing track, until subsequent instructions are received to move the heads to a new address.

The purpose of the landing track and its function is described and claimed in a copending applica-tion assigned to the present assignee and tiled by Welsh, Serial No. 24,950, filed April 27, 1960, now US. Pat. No. 3,200,385.

A positioning mechanism for transporting a carriage along the lsurface of the drums is described in greater detail and claimed in a copending application assigned to the present assignee and tiled hy Marvin Jacoby, Serial No. 23,529, led April 20, 1960, now U.S. Pat. No. 3,225,337.

A contact or collision of ia head with its drum Ais A 3 termed a hit. Hits can be of three types, (l) very short, non-repeated contacts; (2) very s-hort contacts which, however, are repeated periodically, for example, once every revolution; (3) long contacts, which is defined to be contacts 3/4 millisecond or longer in duration.

The rst category of hits can be ignored. However, it is desired to raise the heads 102, 302 when either the second or third types of hits occur. As shown in the gure, normally, the positive potential on the line 203 is transmitted via the heads 102, 302 to the hit detector network to provide nonenabling voltage levels to the buffers 104, 304 and the gates 105, 305. When a head 102 or 302 :hits a drum, the voltage level on the Hit A or Hit B line, respectively, is grounded to provide an enabling signal to its respective buffer 104 or 304 and the gate 105 or 305. Thus, hits with either the drum A or drum B, which are detected by the grounding of the associated head are b-uifed :together to set the delay flop 206 for a period of 75 ms. The 75 ms. period is just slightly longer than a period of one drum revolution. The set output of the delay flop 206 is coupled through the integrator 207, which takes 5A ms. to build up a voltage sufficient to open up the gates 105, 305. The Hit A line is connected to the buffer 104 and the gate 105. The Hit B line is connected lto the buffer 304 and the .gate 305. Thus, when the duration of the contact is less than 32g ms., the signal does not get through the gate 105, 305. When, however, the hit exceeds 74 ms. in duration, the latter portion of the hit passes through the gate 105, 305 to set its respective Hip-flop 108, 308. Likewise, when a hit, though of short duration, is repeated dur-ing the 75 ms. period of the delay flop- 206, it also passes through the gates 105, 305 to set its respective flip-flops 108, 308. The outputs of the flipops 108, 308 are butfed together through :buffers 110, `and 310 and connected to the control network 211. The presence of a hit signal to the control network 211 act-uates the head raising .and lowering mechanism 212 thereby raising the heads 102, 302. Should `a significant hit occur while the carriage is at rest, the heads raise, but the carriage does not move, thus providing the opportunity to fully inspect the area where the carriage is presently located. Should the -hit occur while the carriage is in motion, the heads '102, 302 raise and the carriage travels to the landing strip. In any event, in order to lower the heads 102, 302, a reset or clear 'signal is generated on the line 209, by the operation of a switch, not shown. The carriage travels to the landing strip, if not already there, to place the heads in a flying position. The system is now in condition for the detection of subsequent hits.

Typical characteristics of one embodiment of this invention are given below; other characteristics may be used without digressing from t-he scope of this invention. The storage on one track is 3000 characters, or 21,000 bits. The diameter of the drum is 24 inches. The drum rotates at la speed of 870 revolutions per minute. The bit density per track is 325 p.p.i. A hit is detected when the resistance between head and drum drops below 800 ohms. Various modifications can be made to the circuits which are within the scope of this invention. For example, counting circuits can be added to count the number of hits and to :halt the operation of the system by the accumulation of a predetermined number of hits.

What is claimed is:

1. In combination, a magnetic drum adapted to be rotated, a magnetic head adapted to fly over the surface of said drum and adapted to be retracted away from said surface, a control circuit adapted to raise said head when said circuit is actuated, and means for detecting a collision of said head with said drum and for actuating said control circuit in the event of said collision.

2. In combination, a pair of magnetic drums, a pair of magnetic heads adapted to fly over the surface of said I.drums respectively and :adapted to be retracted away from the surface of said drums, a head raising and lowering mechanism common to both of said heads, a control circuit, said control circuit when actuated adapted to control said mechanism to raise both of said heads, and means for detecting a collision by either one of said heads with its respective drum and for `actuating said control circuit in the event of said collision.

3. In combination, a magnetic drum adapted to be rotated, a magnetic head adapted to fly over the surface of said drum, means for receiving a potential source, means coupling said receiving means to said head so that said head is normally maintained at said potential source, `a delay o-p, means coupling said head to the input of said delay op, an integrator having its input coupled to the output of said delay Hop, a two-input and gate, means coupling said head to one input of said and gate, means coupling the output of said integrator to the second input of said and gate, and a flip-flop having its set input terminal coupled to the output of said and gate.

4. In combination, a detection line, a delay flop having its input coupled to said detection line, an integrator coupled to the output of said delay flop, an and gate having one input coupled to lsaid detection line and having a second input coupled to said integrator, and a ipiiop coupled -to the output of said and gate.

5. A first detection line, -a second detection line, a delay flop, a rst means coupling said first detection line to the input of said delay op, a second means coupling said second detection line to the input of said delay flop, an integrator coupled to the output of said delay flop, a -rst two-input and gate having one input coupled to said rst detection line, `a second two-input and gate having one input coupled to said second detection line, said second inputs of both of said and gates being coupled to said integrator, a first Hip-flop having its set terminal coupled to the output of said rst and gate, a second flip-hop having its set terminal coupled to the output of said second and gate, means for receiving a reset signal coupled to the reset terminals of both of said flip-flops, and means coupling the output terminals of said flip-flops to an output line.

6. A drum having a cylindrical magnetic surface thereon land adapted to be normally rotated about its Iaxis one revolution per interval of time t2, a magnetic transducer head adapted to y over and magnetically cooperate with said surface without normally physically contacting said surface, said head also being adapted to be retracted away from cooperation with said surface, detection means coupled to said head Ibeing adapted to provide lan electrical indication when said head abnormally contacts said surface, the duration of said electrical indication being substantially equal to the duration of said abnormalcontact, tim-ing means being coupled to said detection means for providing a control signal when said electrical indication is present during a time interval tl to t3 immediately following the initiation of `an electrical indication, and retraction means being adapted to retract said head upon the receipt of said control signal, the time t1 being substantially shorter in time than the time l2, the time t3 being slightly longer in time than the time t2, whereby said head is retracted away from said drum whenever said contact exceeds a duration of time l1 and whenever a contact occurs during -an interval t1 to t3 after a previous contact occurred.

7. The combination as claimed in claim 6 wherein said timing means comprises an and gate, a lfirst electrical means coupling said detection means to one input of said and gate, land a second electrical means coupling said detection means to a second in-put of said and gate, said second electrical means comprising a monostable multivibrator having an output time interval of a time t3, and an integrator being coupled to the output 3,290,666 5 6 0f said monostable multivibrator and having a time con- FOREIGN PATENTS stant equal to an intervalof time t1. 804 441 11/1958 Great Britain References Cited by the Examiner UNITED STATES PATENTS 5 TERRELL W. FEARS, Acting Przmary Exammer.

2,760,063 8/1956 Andrews 340 174 1 IRVING SRAGOW, E. R. REYNOLDS, BERNARD 2,772,135 1'1/1956 Holla'baugh 340-1741 KONICK, Exammefs- 2,787,750 4/1957 Jones 34041741 R. A. CAHILL, A. I. NEUSTADT, R. M. JENNINGS,

2,948,884 8/1960 Guerber et al. S40- 174.1 10 

1. IN COMBINATION, A MAGNETIC DRUM ADAPTED TO BE ROTATED, A MAGNETIC HEAD ADAPTED TO FLY OVER THE SURFACE OF SAID DRUM AND ADAPTED TO BE RETRACTED AWAY FROM SAID SURFACE, A CONTROL CIRCUIT ADAPTED TO RAISE SAID HEAD WHEN SAID CIRCUIT IS ACTUATED, AND MEANS FOR DETECTING A COLLISION OF SAID HEAD WITH SAID DRUM FOR ACTUATING SAID CONTROL CIRCUIT IN THE EVENT OF SAID COLLISION. 